Northern Irishman McIlroy has developed a penchant for making fast starts and he did it yet again on a blisteringly hot day at the third major championship of the season, firing a pacesetting six-under-par 66.

Woods, playing in only his third competitive round since undergoing back surgery in March, confounded the critics who wrote off his chances by shooting a 69.

The 14-time major winner made a poor start by bogeying the first two holes but it was almost vintage Tiger on the back nine as he went storming through the field with five birdies in six holes from the 11th.

The former world No. 1, sporting grey slacks and a white shirt with blue/grey flecks down the front, got his round going when he holed out from off the green at the 11th.

Woods then rattled in birdies at the 12th and 13th before dropping a stroke at the 14th following a hook off the tee into thick rough.

The 38-year-old American bounced straight back by sinking a 12-footer at the next hole. A delicate chip to 12 inches from the cup at the 16th gave him another birdie before a long-range effort lipped out on 17.

Interest in Woods ran high with American television network ESPN devoting the whole of its ESPN3 digital channel to coverage of him.

“I knew I could do it. I'm telling you guys it was so important for me to play at Congressional,” he told reporters, referring to his two comeback rounds at the Quicken Loans National event in Maryland last month.

“It felt good to be back out there competing again today. It wasn't exactly the greatest of starts, bogeying the first two, and especially the second hole was a sloppy three-putt.

"Coming back after that start I had today, to fight myself back into the championship. I feel pretty good about it."

Woods did not, however, feel particularly good about some of the distractions from the amateur photographers among the 35,000 crowd and the professional snappers.

"There were a lot of cameras out there," said Woods, rannked seventh in the world. "We were backing off a lot of shots and a lot of people were moving around - that was tough.

“Unfortunately people just don't put their phones on silent or some of the professional guys were getting on the trigger a little early.”

It was McIlroy, though, who took the tournament by the scruff of the neck with some scintillating shot-making.

Taking advantage of benign scoring conditions on a flat course with few undulations, the twice major winner peppered the flag on the front nine.

McIlroy almost holed out with his second shot at the par-four second before converting putts of six and 14 feet for further birdies at the fifth and sixth.

The 25-year-old made more inroads on par at the 10th and 12th before enjoying an outrageous moment of good fortune at the 14th when he avoided trouble in the rough with a lucky bounce on to the fairway.

McIlroy did not drop a shot to par all day and a sixth and final birdie at the 16th took him to the top of the leaderboard.

“We had perfect scoring conditions out there this morning,” said the world number eight. “There wasn't much wind.

"It started to pick up a little on the back nine but there were plenty of opportunities to make birdies and I was able to take a few of them."

Playing in the heart of Liverpool Football Club country, it was perhaps no surprise that Manchester United fan McIlroy was on the receiving end of some Merseyside humour.

"I got terrific support even though I support United," he laughed. "I took my hat off on 16 or 17 walking up the fairway and I heard someone say, 'Get a hair cut.'

“Apart from that the support was really great and hopefully I can give them a lot more to cheer about in the next few days.”